Field of the Invention
The present invention relates to a silicone resin composition for a sealant used for power semiconductor modules, and to a power semiconductor module that uses this composition.
Description of the Related Art
Power semiconductor devices are made into power semiconductor modules by incorporation in a package that exhibits excellent heat-dissipating characteristics and are then used as power converters for, for example, industrial machinery and transportation equipment.
The structure of a general power semiconductor module will be described using FIG. 5. A power semiconductor module 10 is provided with a semiconductor device 1; an insulating circuit substrate 2 that has a first metal layer 2b on a first main side of an insulating substrate 2a and a second metal layer 2c on a second main side; a metal plate 3; a bonding wire 4; an external terminal 5; a case 7; and a sealant 8. The back side of the semiconductor device 1 is bonded to the first metal layer 2b of the insulating circuit substrate 2 through an interposed bonding member 6a, and the second metal layer 2c of the insulating circuit substrate 2 is bonded to the metal plate 3 through an interposed bonding member 6b. The heat generated by the semiconductor device 1 is dissipated by transmission to the bonding member 6a, first metal layer 2b, insulating substrate 2a, second metal layer 2c, bonding member 6b, and metal plate 3 in the indicated sequence and is further transmitted from the metal plate 3 to a cooling device, which is not shown in the figure. The first metal layer 2b is divided into a plurality of island-shaped regions and an electrical circuit is formed by interconnection through the bonding wire 4. In addition, the external connection terminal 5 is bonded by the bonding member 6a to the first metal layer 2b to enable an electrical connection to be made to an external circuit. In order to protect the semiconductor device 1 and the insulating circuit substrate 2 from the external environment, they are housed in the case 7 and sealing is carried out by the sealant 8, e.g., a silicone gel, filled within the case 7.
Japanese Patent Application Laid-open No. 2012-36274 describes a semiconductor module sealant that is resistant to peeling and cracking even when heated; it is a mixture of a strongly branched organopolysiloxane and a weakly branched organopolysiloxane as obtained by varying the ratio between the difunctional siloxane units and trifunctional siloxane units that constitute an organosiloxane. In addition, the results are given for tensile shear testing and for the dielectric strength after a temperature cycling test.
Japanese Patent Application Laid-open No. H8-269331, on the other hand, describes a silicone gel composition for potting applications that cures by crosslinking through an alcohol-eliminating condensation, ketone-eliminating condensation, or dehydrocondensation. It is also stated that the penetration, which indicates the hardness of the silicone gel, undergoes almost no change even during exposure for 300 hours to O3 and NOx generated by a spark discharge.
Japanese Patent Application Laid-open No. 2008-270469 discloses a semiconductor module structure in which a semiconductor device and an insulating circuit substrate are sealed by a silicone gel and the silicone gel is then additionally coated with a thermoplastic resin (for example, an epoxy resin). It is also stated that defects such as voids, cracks, peeling, and so forth were absent when inspection was performed with an ultrasound imaging device after a high-temperature, high-humidity test (85° C., 85% RH).